1. Field of the Invention
This invention relates to a piston and cylinder type thermal device and method of making the same as well as to a resilient stem seat for such a device and method of making the same.
2. Prior Art Statement
It is known to provide a substantially pure push type thermal device having a resilient stem seat provided with an opening in one end thereof and receiving an actuating stem in the opening that is adapted to reciprocate in the opening in response to the thermal expansion and contraction of a charge of material in the device and operatively acting on the stem seat adjacent the other end thereof.
For example, see the following U.S. patent:
(1) U.S. Pat. No. 3,046,787--Wagner PA1 (2) U.S. Pat. No. 3,016,747--Vernet PA1 (3) U.S. Pat. No. 3,080,756--Baker
It appears that the resilient stem seat of item (1) above has the diameter of the opening therein substantially the same as the diameter of the actuating stem being received therein except that a narrow section of the stem seat adjacent to the open end of the opening has a reduced diameter through which the stem is press-fitted to not only form a seal between the stem and the stem seat, but also between the stem seat and the casing carrying the same.
Another known type of thermal device comprises a squeeze-push type wherein the resilient stem seat has a considerable length thereof radially surrounded by the charge of material which, when expanded, will squeeze the stem seat radially inwardly to squeeze and, thus, push the actuating stem relative to the stem seat.
For example, see the following U.S. Patent:
It appears that the opening in the resilient stem seat has a diameter less than the outside diameter of the actuating stem so that the actuating stem must be press-fitted in the opening of the stem seat substantially throughout the entire length thereof during the assembly of the stem within the stem seat.
Another known type of thermal device comprises a substantially pure squeeze type wherein the resilient stem seat has substantially the entire length thereof radially surround by the charge of material which, when expanded, will squeeze the stem seat radially inwardly to squeeze and, thus, push the actuating stem relative to the stem seat.
For example, see the following U.S. Patent:
It appears that the resilient stem seat of item (3) above is formed with the stem diameter and the stem seat diameter such that the cross-sectional area of the enclosing wall is equal to or greater than the area of the cavity within the elastic stem seat body so that there are only small stresses upon the walls of the elastic stem seat body during expansion of the charge in the device.